From the official website of the United States Marine Corps:
The Marine Corps Silent Drill Platoon is a 24-man rifle platoon that performs a unique precision drill exhibition. This highly disciplined platoon exemplifies the professionalism associated with the United States Marine Corps.
The Silent Drill Platoon first performed in the Sunset Parades of 1948 and received such an overwhelming response that it soon became a regular part of the parades at Marine Barracks Washington, D.C.
The Marines execute a series of calculated drill movements and precise handling of their hand-polished, 10-and-one-half pound, M1 Garand rifles with fixed bayonets. The routine concludes with a unique rifle inspection sequence demonstrating elaborate rifle spins and tosses.